1. Technical Field
The invention relates to air conditioner compressor control systems, and particularly to a vehicle air conditioner system control method and apparatus that prevents a system compressor from decreasing in speed, or altogether stopping, due to high pressure cycle conditions, with the system having particular application in an electric vehicle heat pump system.
2. Related Art
In Japanese Unexamined Patent Publication No. Hei. 9-86149, a vehicle heat pump system having a gas injection cycle for increasing heating capacity in an air-conditioning apparatus for an electric car has been proposed.
In such a system, the amount of gas injected to an electric compressor is increased to increase heating capacity at times of low outside air temperature. The amount of injected gas is increased by opening the aperture pressure-reduces high-pressure refrigerant to an intermediate pressure at times of heating capacity deficiency, to increase the intermediate pressure. As a result, the compression work of the electric compressor is increased, and the amount of heat released by refrigerant in an inside heat exchanger is increased.
And, when a detection value of a current sensor for an inverter for electric compressor speed control rises to a predetermined value, the aperture of the high-pressure side electric expansion valve is reduced to prevent overloading of the inverter.
However, in the above-described expansion valve control, if the use limit of the inverter is exceeded, an inverter protection control function works, and the compressor speed is lowered, or compressor (cycle) stoppage occurs. This often occurs during heating when the high pressure of the cycle is liable to rise, such as when the airflow into the compartment is low or the temperature in the compartment is high, because compressor torque rises as a result of a sudden rise in the high pressure. This result may occur even if the aperture of the high-pressure side electric expansion valve is reduced from when the current value of the inverter is detected to have risen above a predetermined value.
In more detail, the vertical axis of FIG. 23A is output current (inverter line current) of an inverter for electric compressor speed control and cycle high pressure. At times of heating, under conditions such as when the airflow delivered into the compartment is low and when the temperature in the compartment is high, or at times of switching from an outside air intake mode to an inside air intake mode, because the compressor torque rises due to a sudden rise in high pressure, the increase in the inverter current is great.
Consequently, even if the high-pressure side electric expansion valve starts to close when the inverter current is detected to have exceeded a first determination current value g at time t.sub.1 shown in FIG. 23, because the behavior of the cycle cannot immediately follow the reduction in the expansion valve aperture, the rise of the high pressure cannot be immediately suppressed. Over a short time period from time t.sub.1 to time t.sub.2, the high pressure continues to rise.
Consequently, the inverter current also continues to rise over the period from time t.sub.1 to time t.sub.2, and often it may exceed second, third determination current values h, i of the region of inverter protection control.
Here, when the inverter current exceeds the second determination current value h, control that lowers the compressor speed is carried out. When the inverter current exceeds the third determination current value i, the compressor is stopped.
As a result of the lowering of the compressor speed, or of compressor (cycle) stoppage occurring, heating draft air temperature decreases, thereby reducing passenger compartment heating effectiveness.